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United States Patent |
5,741,262
|
Albrektsson
,   et al.
|
April 21, 1998
|
Hip joint prosthesis
Abstract
The invention relates to a hip joint prosthesis comprising an attachment
part for a ball unit (18) being designed to be anchored in the neck of a
human femur (collum femoris), said attachment part, which is intended to
be inserted into a channel (5, 14) extending through the femoral collum,
being provided with parts for carrying a ball or caput (18) intended to be
attached to the collum after removal of the head of the collum. The
attachment part also comprises a fixture part comprising two main parts, a
first part (1) which is to extend through a bore-hole (5) from the collum
femoris towards the outer side of the femur and a second part (2) intended
to fit into a cylindrical cavity cut into the cancellous bone of the
collum.
Inventors:
|
Albrektsson; Bjorn (Gothenburg, SE);
Jacobsson; Magnus (Gothenburg, SE);
Carlsson; Lars (Kullavik, SE);
Rostlund; Tord (Kullavik, SE);
Wennberg; Stig (Angered, SE)
|
Assignee:
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Astra Aktiebolag (Sodertalje, SE)
|
Appl. No.:
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473564 |
Filed:
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June 6, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
606/80 |
Intern'l Class: |
A61B 017/56 |
Field of Search: |
606/89,86,96,80,79
623/18,22,23
|
References Cited
U.S. Patent Documents
2682265 | Jun., 1954 | Collison.
| |
2685877 | Aug., 1954 | Doselle.
| |
2785673 | Mar., 1957 | Anderson | 606/96.
|
3002514 | Oct., 1961 | Deyerle | 606/96.
|
4005495 | Feb., 1977 | Locke et al.
| |
4795473 | Jan., 1989 | Grimes.
| |
4976740 | Dec., 1990 | Kleiner.
| |
5342363 | Aug., 1994 | Richelsoph | 606/79.
|
5376125 | Dec., 1994 | Winkler.
| |
5429641 | Jul., 1995 | Gotfried | 606/67.
|
Foreign Patent Documents |
2438470 | May., 1980 | FR.
| |
2674122 | Sep., 1992 | FR.
| |
2724234 C2 | Dec., 1977 | DE.
| |
2854334 B2 | Jun., 1980 | DE.
| |
3420035 A1 | May., 1984 | DE.
| |
WO 91/07932 | Jun., 1991 | WO.
| |
Primary Examiner: Tucker; Guy V.
Attorney, Agent or Firm: White & Case
Parent Case Text
This application is a divisional of application Ser. No. 08/290,915, filed
Aug. 22, 1994, still pending, which is a U.S. national stage application
of International application No. PCT/SE93/00169, filed Feb. 26, 1993.
Claims
We claim:
1. A method for permanent anchoring of a fixture for a hip joint prosthesis
in the neck of a human femur comprising the steps of:
resecting the head of the femur to expose a section of the femur neck,
drilling into the femur neck through the exposed femur neck section in a
predetermined forward direction towards a position below the greater
trochanter to form a cylindrical bore in the femur neck which extends in
the predetermined forward direction and which is stepped into a rearward
portion of a first diameter having an open end in the exposed femur neck
section and a coaxial forward portion of a second diameter less than the
first diameter extending forwardly from the rearward portion,
providing a fixture having a cylindrical anchoring portion of stepped screw
threaded outer surface profile and diameters corresponding essentially to
those of the bore, and
anchoring the fixture in the femur neck by inserting the cylindrical
anchoring portion of the fixture into the bore by translation of the
fixture in the predetermined forward direction.
2. A method according to claim 1, wherein the first diameter of the
rearward portion of the bore is so selected that cortical bone from the
outer peripheral layer of cortical bone in the femur is presented in the
boundary wall of the rearward portion of the bore for screw threads on the
outer surface of the cylindrical anchoring portion of the fixture to
register in.
3. A method according to claim 2, wherein the first diameter of the
rearward portion of the bore is so selected that the circumference of the
rearward portion of the bore contacts the outer peripheral layer of
cortical bone in the femur in at least three circumferentially spaced
locations.
4. A method according to claim 1, wherein the bore is formed by drilling a
first bore having the second diameter in the predetermined forward
direction through the exposed femur neck section into the femur neck
towards a position below the greater trochanter and then drilling a second
bore having the first diameter in the predetermined forward direction
through the exposed femur neck section coaxially with the first bore to a
position between the exposed femur neck section and the forward end of the
first bore.
5. A method according to claim 4, wherein the second bore is formed by
providing a drill having a cylindrical forward guide section of
essentially the second diameter and a coaxial rearward drill section for
drilling the second bore, inserting the guide section of the drill into
the open end of the first bore in the exposed femur neck section and
translating the drill in the predetermined forward direction under the
guiding action of the guide section until the drill section of the drill
reaches the position between the exposed femur neck section and the
forward end of the first bore.
6. A method according to claim 5, wherein the rearward drill section
includes grinding means which on translation of the drill in the
predetermined forward direction grinds the exposed femur neck section to a
plane which is orthogonal to the predetermined forward direction.
7. A method according to claim 1, wherein the bore is formed so as to
extend in the predetermined forward direction between the open end in the
exposed femur neck section and an open end in the femur outer surface
positioned below the greater trochanter.
8. A method according to claim 1, wherein the screw threads on the outer
surface of the cylindrical anchoring portion of the fixture are
self-tapping.
Description
TECHNICAL FIELD OF THE INVENTION
The invention relates to a hip joint prosthesis for permanent anchoring in
the human hip joint comprising an attachment part for a ball unit designed
to be anchored in the neck of a human femur (collum femoris), said
attachment part, which is intended to be inserted into a channel extending
through the femoral collum, being provided with parts for carrying a ball
or caput intended to be attached to the collum after removal of the head
of the femur.
BACKGROUND OF THE INVENTION
The present invention is a development of a hip joint prosthesis of the
kind disclosed in WO 89/11837. This document inter alia discloses a hip
joint prosthesis comprising a primary fixture in the shape of a sleeve,
said sleeve being intended to be inserted into a central hole bored
longitudinally through the collum femoris from the outer side of the femur
and a secondary fixture in the shape of a cap having a spherical shape
intended to be attached to and cover the end of the collum femoris when
the head of the collum has been removed partly or entirely and the outside
of remaining end has been cut to a cylindrical shape. The primary and the
secondary fixtures are interconnected by means of a bolt which at one end
has an internal thread. The bolt is to be inserted into the sleeve and its
internal thread is to be made to engage a central, threaded stud
projecting from the spherical cap. When the bolt is tightened, the cap is
pressed over the cylindrically cut caput or end of the collum.
The prior art device thus is relatively complicated, both in construction
and use.
In some applications it may furthermore not be suitable to use this prior
art device. One reason for this is that the shape of the collum may make
it difficult to retain enough cortical bone to give the secondary fixture
or cap a firm support, since the shape of the collummay vary to a great
extent.
This prior art device is also designed to be inserted in a two-seance
procedure, i.e. some parts of the prosthesis are to be inserted in a first
operation, the remaining parts being inserted later in a second operation
after a healing period of a few months.
Other similar prior art is disclosed for instance in DE-A1-28 45 231,
DE-A1-27 24 040, U.S. Pat. No. 4,795,473 and U.S. Pat. No. 4,005,495.
The object of the invention is to achieve a hip joint prosthesis which is
simple in construction and use and which is particularly suited for
insertion in a one-seance operation and which can be adapted to fit
different conditions.
BRIEF DESCRIPTION OF THE INVENTIVE CONCEPT
According to the invention the attachment part in a hip joint prosthesis of
the kind described above also comprises a fixture part comprising two main
parts, a first part which is to extend through a bore-hole from the collum
femoris towards the outer side of the femur and a second part intended to
fit into a cylindrical cavity cut into the cancellous bone of the collum.
The fixture can be made in one piece but, in one preferred embodiment,
comprises two separate parts which are firmly attached to each other
before the fitting of the fixture into the femur.
This will result in that the cortical bone will remain intact to a larger
degree and that the load conditions will be such that a physiologically
appropriate load on the upper part of the collum can be achieved. Forces
can be transferred from the fixture to the femur without any noticable
movements by means of the direct or indirect contact with the inside of
the cortical bone in the collum.
BRIEF DESCRIPTION OF THE APPENDED DRAWINGS
FIG. 1 is a section of a femur with the fixture mounted, the femur but not
the fixture being sectioned,
FIG. 2 illustrates a confined reamer and cutter for shaping the recess in
the collum for the fixture,
FIG. 3 illustrates the shape of the recess in the collum, and
FIGS. 4 and 5 show a section of the collum with the recess with and without
the fixture.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
As can be seen in FIGS. 1 and 5, the fixture comprises two main parts, an
elongate, cylindrical first part 1 and a second plug-like, generally
cylindrical part 2. The first part 1 is provided with relatively large and
widely spaced threads 3 on a major or main part of its outside, the
remainder 4 of its outside being smooth and slightly conical. On the end
surface of the slightly conical end of the first part 1 a narrow, threaded
part 17 is located which is coaxial with the first part 1.
The first part 1 is to fit in a channel or hole 5 drilled longitudinally
and centrally through the collum 6. The head 7 of the first part 1 is to
be located on the outside of the femur and may, but need not (of FIG. 5),
be locked against rotation by means of an elongate plate 8 having a recess
9 with a shape complementary to the shape of the head 7 of the first part
1. The elongate plate is attached to the femoral shaft by means of screws
10. The head 7 of the first part may, but again need not, also be covered
by means of a nut 11 having threads being complementary to the threads 3.
A longitudinal bore being provided with threads is provided in the end
surface or head 7 of the first part 1. This bore is complementary to a
threaded tap on a guide rod having the same diameter as the first part.
The second part 2 is in the shape of a cylindrical plug. One part 12 of the
plug is to be inserted into a recess 14 cut in the collum, cylindrically
and co-axially with the channel or hole 5. The outside of the part 12 of
the plug is provided with threads 15 similar to the threads 3 on the first
part 1. The plug 12 is delimited by a circumferential flange 16 limiting
the insertion of the plug 12 into the cavity or recess 14. The plug 12
further is provided with a central hole 26 having two parts, an inner,
threaded part 27 having an inner diameter corresponding to the outer
diameter of the threaded narrow part 17 of the first part 1 and an outer,
unthreaded part 20 which is slightly conically flaring in a way
corresponding to the unthreaded part 4 of the first part 1 of the fixture.
The threaded parts 17, 27 as well as the threaded parts 1, 12 may be
right-handed or left-handed depending on which side of the body they are
to be mounted.
The threads on the first and second parts preferably are self-tapping. This
can for instance be achieved in that the distal ends of the first and the
second part are provided with sharpedged recesses 21, 22 in a manner
similar to self-tapping screws. The recesses 22 on the second part 2
extend all the way to the end surface of the second part. The recesses 21
on the first part 21 do however not extend all the way to the end surface
or head 7, since this part of the first part 1 normally is to be located
in the soft tissue and for this reason should not have any sharp edges.
This is especially important if no covering nut 11 is used.
The first part 1 is made in several versions with different lengths and the
second part 2 is made in several versions with different diameters of the
plug part 12.
The plug finally is provided with a conical projection or attachment cone
13 for carrying the ball or caput 18 which is provided with a
complementary conical hole 19.
The first and the second part of the fixture preferably are made of c.p.
(commercially pure) titanium and may be subjected to a suitable surface
treatment. The elongate plate 8 preferably is made of a suitable titanium
alloy, whereas its attachment screws 10 preferably should be made of c.p.
titanium and for instance have a diameter of 4.5 mm. The attachment cone
can be made of a titanium alloy or of c.p. titanium and should be treated
in a suitable way to minimize the risk for fretting corrosion. The caput
preferably should be made of a ceramic material, also in order to minimize
the risk for fretting corrosion.
The socket or acetabulum is not part of the present invention and may be of
any commerciably available kind which is suitable.
The operation for implanting the hip joint prosthesis is preferably
performed in a one-stage operation.
Any differences in the length of the legs are measured. An estimate of the
narrowest diameter of the collum is made in order to obtain an idea of the
size of the implant to be used.
With great care not to disturb the blood circulation, the hip is exposed
through an anteriolateral approach. The hip joint is then dislocated. A
guide instrument for a cutting tool is attached. The caput is then cut off
and removed.
The narrowest part of the collum is measured directly in order to obtain
further information regarding the size of the implant.
A drill is then oriented by means of the guide instrument in such a way
relative to the surface of the section that the drill is aligned with the
longitudinal extent of the collum and is located at the center of a circle
which touches the inside of the cortical bone in the section in at least
three points. The diameter of this circle is determined. A hole 5 having a
diameter corresponding to the diameter of the first part 1 is then drilled
through the collum from the surface of the section, cf FIG. 2.
The cylindrical recess or hole 14 is then cut longitudinally in the collum
from the direction of the caput by means of a rotary cutting (milling)
tool 23. The cutting tool is provided in several sizes, each size
corresponding to one size of a second part.
The cutting tool comprises a cylindrical, elongate guide part 24 which has
a diameter corresponding to the diameter of the hole 5. The tool further
comprises a reamer 25 which is coaxial with the guide part 24, the
diameter thereof being chosen to correspond to the diameter of the above
circle touching the cortical bone. The diameter and the length of the
reamer also corresponds to one of several standard sizes of the second
part 2. The tool 23 finally also comprises a surface cutter 26.
The guide 24 is inserted into the hole 5 until the reamer 25 engages the
surface of the section. The cylindrical recess 14 is then cut by means of
the reamer until the surface cutter 26 engages and machines the surface of
the section. The object of this machining is to ensure that the surface of
the section is smooth and is oriented orthogonally relative to the
longitudinal axis of the hole 5. This is important since the longitudinal
direction of the collum not necessarily is orthogonal relative to the
surface of the section. The resulting cavity 5, 14 can be seen in FIG. 3.
A first part having a suitable length and a second part having a suitable
diameter are then chosen and attached to each other by means of the
threaded part 17 on the first part 1 and the threaded hole 27 in the
second part. The respective conically shaped parts 4, 20 on the first and
the second part will ensure a secure and tight connection between the two
parts.
The above-mentioned guide rod or extension, which has a diameter
corresponding to the diameter of the hole 5, is then mounted on the free
end of the first part 1 by means of the threaded bore therein. The guide
rod is then inserted into the hole 5 until the threads on the first or the
second part engage the bone tissue in the collum. The fixture is then
screwed into the hole 5 and the recess 14 whilst being kept aligned by
said guide, threads simultaneously being cut into the bone tissue on the
inside of the hole 5 and the recess 14 in the collum until the flange or
collar 16 abuts the cortical bone on the cut end surface of the collum.
Due to the machining by means of the cutter 26, the flange or collar 16
will fit snugly against the surface of the section. The guide rod is then
removed.
Finally a ball or caput 18 is mounted on the attachment cone 13 and a
reduction or repositioning of the joint is made in order to test the
stability of the joint and the length of the leg. The length of the leg is
corrected by using caputs having differently sized conical holes 19. The
operation is then completed.
After the operation the hip joint soon can be subjected to loads to a
limited extent since the design of the fixture will ensure that the
fixture is stable to an extent which is sufficient to allow
osseointegration.
Possible modifications of the invention
The invention of course can be varied in many ways within the scope of the
appended claims.
As mentioned above, the fixture can be made in one, integral part, which
may be advantageous in some applications even if it might greatly increase
the number of different types to be kept in stock.
It is also possible to allow the first part of the fixture to end in the
cancellous bone tissue before it reaches the cortical bone tissue on the
outside of the femur, which may eliminate the necessity of disturbing the
cortical bone and the soft tissue on the outer side of the femur.
It may not always be necessary to achieve the three-point contact between
fixture and cortical bone in the collum femoris discussed above. This may
be of particular importance if the collumfemoris has such a shape that it
more or less is impossible to obtain said three-point contact. In some
cases it may also be more important to center or orient and size the
fixture in such a way that a maximal bone contact is obtained. In one
extreme it might also be conceivable to design or choose the first and
second part of the fixture to have the same diameter. However, if the
lateral femoral cortex is to be penetrated, the diameter of the first part
should be kept at a minimum.
To express the advantages of the device somewhat differently, the hip joint
prosthesis as set forth in the appended claims provides a cylindrical,
longitudinal fixture which may be centered in the collum femoris. This
allows a dimensioning of the device permitting a maximal bone contact
whilst minimizing the risk of perforating the cortical bone in the collum
femoris. The fixture permits the penetration of the lateral femoral cortex
by means of a threaded extension thereof which may have a smaller diameter
than the rest of the fixture. The fixture may have a flange or abutment
collar which may be made to fit exactly against the cut end of the collum
femoris by means of a guided bone cutting tool. The fixture can be
positioned by means of a drill guide permitting the above centering in
conjunction with a centering guide. This, in conjunction with a
self-tapping design of the fixture, preferably in pure or almost pure
titanium, allows the achievement of an optimal bone contact.
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